I think you can cut Urza's Saga without losing out on much
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The satisfaction that arises from slamming a Choke, staring your opponent down in the gut of their eye and passing back knowing they cant do anything for the rest of the damn game
Credit: Wizards of the Coast Capricious Sliver FromTheShire: One of the biggest problems you can run in to with tribal decks, which are inherently creature heavy, is dumping out your hand quickly and becoming the threat, and then failing to draw gas to close out the game
Other options include artifacts to sacrifice, like Eggs and Braids, Cabal Minion
It is worse than a fifth Negate would be, but not by so much that you arent still excited to be bringing it in during sideboarding